1. Field of the Invention
This invention relates to two-dimensional finite impulse response filters.
2. Description of the Prior Art
It is known to use two-dimensional finite impulse response (2D FIR) filters to effect two-dimensional filtering of an input data signal that comprises a stream of digital words and that is representative of a two-dimensional image. The signal may, for example, be a television or video image. As is known to those skilled in the art, and as is explained more fully hereinbelow, a 2D FIR filter is operative to process successive sets of consecutive words of the input signal, each successive set being offset by one word from the preceding wet, to generate successive words of a filtered output signal. The processing involves the use of adders and multipliers, each multiplier being operative to multiply a word by a weighting coefficient. The operations performed by the multipliers and adders take time. For input signals having a low data rate, the operating times of the multipliers and adders are insignificant. Accordingly, an FIR filter can, in this case, comprise a single multiplier and a single adder and means for causing each of a plurality of multiplication and summing operations to be performed sequentially by the single multiplier and single adder during the processing of a set of consecutive words of the input signal. At higher data rates, at which the operating times of the multiplier and adder become significant, this becomes impossible. As the input signal data rate increases, it becomes necessary to employ a single multiplier and a single adder for each computational step. However, as the input signal data rate is increased further, it will transpire eventually that the filter will fail to operate because the signal is too fast to be processed by the slowest components of the filter. (Usually, but not always, the slowest components are the multipliers). That is to say, conventional 2D FIR filters have a maximum operating rate which is determined by the slowest operating components thereof, and cannot process a signal having a data rate higher than the maximum operating rate.